In the field of the embedded applications, correct behavior of a microcontroller typically depends, inter alia, upon a timely response to an external stimulus. Indeed, failure by the microcontroller to respond to an event within an expected time frame can result in serious malfunction of a system that is under the control of the microcontroller. In this respect, response time of the microcontroller is dependent upon hardware and software design and can be an extremely complex value to predict.
Hence, for some embedded applications, a maximum time limit is typically attributed to a given external stimulus, and failure by the microcontroller in some circumstances to respond to the given external stimulus within the maximum time limit results in incorrect performance of the system. In such circumstances, it is desirable to place the microcontroller in a known “safe” state. In other circumstances, failure by the microcontroller to respond to the external stimulus within the maximum time limit can result in the external stimulus becoming invalid after expiration of the maximum time limit. Consequently, providing a response to the external stimulus that is no longer valid can also cause the system to behave incorrectly, for example, becoming stuck in reset.
In order to overcome such problems described above, it is known to design microcontrollers with watch dog functions or elaborate other defensive measures to detect and report timeout events. Once a timeout event is detected, corrective action can be taken to avoid incorrect performance of the system.
The use of the same reference symbols in different drawings indicates similar or identical items.